Which one of the following is discrete data?
a) height if a tree
b) time taken to change a light bulb
c) number of people in a room
d) weight of a baby

C) Number of people in a room is a discrete data.  

Step-by-step explanation:

Discrete Data is defined as the data than can only take certain values.

The values in the discrete data can not be continuous.

Now,

A) Height of a tree : A tree can be of any length and hence is NOT a discrete data.

B) Time Taken to change a bulb : This time taken to change the light bulb may vary from person to person. Hence it is NOT a discrete data.

C) Number of people in a room: This is a discrete data as the number of people can not be in fractions.

D) Weight of a baby : This is NOT a discrete data as the weight of a baby may vary with time. It can increase and decrease with time.